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Steve, Auto Service Technician
Category: Car
Satisfied Customers: 5494
Experience:  25+ yrs experience as a professional working technician; ASE L1 master technician
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I have a 2000 Nissan Maxima with a code of P0430, Catalysts ...

Customer Question

I have a 2000 Nissan Maxima with a code of P0430, Catalysts efficiency below threshold, bank 2. What is causing this & what is needed to repair
Submitted: 10 years ago.
Category: Car
Expert:  Steve replied 10 years ago.


This code is set when the rear oxygen sensor signal closely mirrors the front oxygen sensor signal. THere is an oxygen sensor in front of and also to the rear of the catalytic converter. When the CAT is operating normally, it uses up almost all of the free oxygen available in the exhaust stream in the chemical reaction that takes place to turn CO into CO2. If the rear oxygen sensor shows the same amount of oxygen in the exhaust both before and after the CAT, this is ian indication that the CAT is not doing it's job efficiently.

The only way to repair this is to replace the faulty catalytic converter with a new one of the correct size and type.

This code can also be set if the cat has been replaced with an incorrect one that is too small for the vehicle and therefore is working inefficiently. (the replacement ones sold in discount parts stores such as Autozone or Advance are often universal types that do not perform well on the vehicle; they contain less catalyst material which is why they are cheap).

I hope this is helpful; if so, please click my accept button and leave positive feedback! Thanks!

Customer: replied 10 years ago.
Reply to Steve7654's Post: Does this mean that the cat is actually defective or that the sensor may be defective?
Expert:  Steve replied 10 years ago.

No, the sensorsare working fine; they are both sending matching signals to the ECM... that is what sets the code. The signals will not match each other if the CAT is working normally. A faulty sensor will not cause this code.

You need to replace the catalytic converter, and determine why the original CAT failed to prevent a repeat failure. usually a CAT fails due to an ignition misfire, or a very rich running condition at some point.

You may want to check with the dealer before doing any repairs; new vehicles have federally mandated emission warranties that cover catalytic converter replacement. The warranty period varies by model year and vehicle, but some are as long as 8 years/ 80,000 miles. You should call teh dealer to check what the warranty is on your particular vehicle before spending several hundred dollars on a new CAT; you may be able to get it replaced for free.

Customer: replied 10 years ago.
Reply to Steve7654's Post: I do appreciate the info, but I took the car to a dealer on Saturday and checked everything out. They replaced the sensor, they said the sensor was defective and replaced it. The engine light has not been on since. I asked them what you had told me, they said it is possible but not probable. Their experience is this sensor being defective.
Expert:  Steve replied 10 years ago.

If the code is as you described (catalyst efficiency below threshold), tehn there is no possible way for the sensor to be defe3ctive; if order for this particular code to store, the bank 2 post catalyst sensor has to be operational. The code stores when the signal exactly matches the pre-cat O2 signal. A defective sensor produces *no* signal, which sets a completely different code than the one you described... a defective post cat oxygen sensor is not even one of the possible causes listed in the manufacturer's diagnostic charts for this code.

I'm not sure what to say; either the dealer has misdiagnosed the problem and the code will eventually return, or the initial code that was described is not the actual code that was stored; but there is no possible way for a faulty post cat O2 sensor to cause a catalyst efficinecy code to store...

Sorry I couldn't be more helpful, bit if the code returns after a few days let me know... I suspect it may, since when the dealer erased the stored codes they also by necessity erased all catalyst monitor data from computer memory. it may take up to a week for the catalyst monitor self test to re-run in the vehicle, depending on your driving habits. The code will not reset untill the catalyst monitor runs again.